Conductive bioink

Development of an electrically conductive bioink

To go further in organ model development in 3D bioprinting, several bioink still need to be created. A conductive bioink was one of them. Achieving a physiological relevant conductivity for different use will open new possibilities for whole organ model development, such as nerve repair with new possibilities for tissular regeneration. Additionally, it can be used for muscular contraction models where after electric stimulation, cells can contract, leading to a functional muscle.

Aim

Printing protocol

A printing protocol of the GelMA based bioink has been optimized for both Inkredible+ and Bio X, equipped with a cooled print head. After a quick preparation, the bioink can be mixed with cells and printed with a high precision (0.35 mm). Afterwards, the bioink can be cross-linked with UV light without lowering the viability.

Electrical conductivity

The conductivity is important to allow cells to communicate electrically to one another. Carbon nanotubes are remarkably conductive, leading to low concentrations, and no change in bioink behaviour.

Viability

The viability after printing, both Day 1 and Day 14, has been assessed for Human Dermal Fibroblasts (HDFs) and more sensitive Neural Progenitor Cells (NPCs). The viability for HDFs was at Day 1 80% and Day 14 at 95%. NPCs are like mentioned a sensitive cell type leading to the viability of Day 1 being 44% and at Day 14 22%. However, the cells tend to cluster which is not accounted for in the live/dead analysis.

Validation experiment

A follow-up validation study of the conductive bioink was performed to evaluate the reproducibility. In line with previous studies, the conductive bioink shows good viability of sensitive NPCs. In addition, a new variation of the bioink was tested which showed increased stretching of the NPCs. Already at day 7 after printing there was a visible difference between the two conductive bioinks, with more NPCs reaching out to each other in the new variation instead of clustering together.

The images beside shows viability staining at day 7 for the two conductive bioink variations, both in grayscale and labeled with green (live cells) respectively red (dead cells). In the left column of images, displaying NPCs in conductive bioink, clusters are clearly visible. In the right column of images, displaying NPCs in the new variation of conductive bioink, there are less clusters and more cells aligned with the structures of the 3D matrix. Showing that stretching and spreading of cells through the 3D constructs in the conductive bioink can be enhanced by additional components.

Conclusion

In this study, the new CELLINK Conductive bioink demonstrate high precision while printing and a great conductivity had been achieved. It has also been shown that both HDF and NPC can be mixed in the bioink and cultured for 14 days. CELLINK Conductive ink is therefore appropriated to new models.